In our European patent application No. 85.200.130.4, corresponding to U.S. Pat. No. 4,593,554, there is described a method of rapidly showing any leakage in vacuum packages. According to a preferred embodiment of that application, a flexible bell is placed within a rigid bell. The vacuum package is placed in the flexible bell, which consists of flexible, elastic foil, whereafter a pressure differential is provided between, on the one hand, the space between the vacuum package and the flexible bell and, on the other, the space between the rigid bell and the flexible bell, to cause the foil of the flexible bell to fit closely around the vacuum package.
The pressure in the small space remaining between the vacuum package and the flexible bell is kept higher than the pressure in the vacuum package. In the event of a leakage, air will pass from the small remaining space into the vacuum package. As a consequence the pressure in this small space will decrease. This decrease can be measured in a highly sensitive manner.
The preferred embodiment referred to above is shown in FIG. 3 of the above European application and is a (e.g. rubber) bag having substantially the same shape as the vacuum package to be tested.